For many years, in the United States and Europe, one way of treating sewage has been to provide a plurality of rotating discs partly submerged in the wastewater, which discs are located on a shaft and are spaced apart a sufficient amount to permit biological growth on the discs, yet will permit sloughing of the growths. The discs which have been generally flat or slightly raised have been limited in diameter due to shipping limitations. The work that has been done in this area is directed towards treating wastewater, and it is known that using partially submerged rotating discs or drums there is provided a very suitable surface for the growth of biological slimes by exposing them alternately to the atmosphere to gain the oxygen necesary for their respiration and then immersing them in the wastewater for the bioextraction of pollutants for their nutrition. While this concept has been known for many years, it has not been particularly successful, since it has not been possible to get the degree of treatment necesary to economically justify the expense of such apparatus. It is acknowledged that even though rotating biological contactors have been used for many years, new interest is being shown in them, as evidenced by a large number of U.S. Pat. Nos. issued to such companies as Autotrol Corporation of Milwaukee, Wisconsin (Torpey 3,915,854, Antonie 3,704,783, Torpey 3,776,841, Prosser 3,886,074, and numerous others) Environmental Pollution Control Co., Inc. (Joost 3,630,366) and various other U.S. and foreign companies. The resurgence of activity is believed to result from the existence of new plastics and the high energy costs of other systems being currently employed.
In the normal rotating biological contactor system, neither the water, nor the air is moved artificially. Only the biomass growing on the discs is exposed intermittently to the air and the water. The energy required by the emerging portion of the biological growth is compensated for the portion submerging at the same time. The actual amount of power required is used to overcome friction losses of the disc system and to compensate for weight differences between emerging and submerging disc sections. The energy consumption of this process is lower than for many other methods.
It is a primary purpose of the present invention to provide an apparatus that will overcome some of the disadvantages of prior constructions so as to make it more economically and mechanically feasible. It is believed that the present invention will provide apparatus for upgrading existing primary or secondary wastewater treatment plants to remove a substantial fraction, if not virtually all of the carbonaceous BOD being discharged in the effluent. Essentially, it is an object of this invention to provide apparatus that will be more economicaly feasible and reach wide-scale acceptance due to the advantages and efficiencies it offers to treatment plants. The novel apparatus is especially applicable to the nitrification stage that is being added to new plants.